   <script src="./vue.js">

    </script>
    <div id="app">
        <div v-bind:class="{box}">我是box
            <div v-bind:class="{inner}">我是inner1</div>
            <div v-bind:class="{inner}">我是inner2</div>
        </div>

    </div>
<script>
    var vue = new Vue({
        el: "#app",
        data: {
            box: 'box',
            inner: 'inner'
        }
    })
</script>

<style>
    .box {
        background-color: pink;
        width: 100%;
        height: 100%;
    }

    .inner {
        background-color: red;
        width: 80px;
        height: 100px;
    }
</style>